1. Field of the Invention
The present invention relates to a system for measuring temperatures in reactors operated at high temperatures and under pressure, such as reactors burning coal dust in power plants or pressurized coal-gasification plants, by the use of a pyrometer.
2. Discussion of Prior Art
The gasification of bituminous coal or lignite involves its partial combustion with oxygen or oxygen-containing gases in the presence of water to give mixtures of carbon monoxide and hydrogen. In the process, powdered coal or coal dust is reacted at temperatures ranging from about 900.degree. to 1600.degree. C., and preferably from 1100.degree. to 1500.degree. C., and elevated pressures of up to 200 bars, and preferably between 5 and 100 bars. This operation is advantageous mainly because modern mechanized coal-mining methods result in an increasing volume of coal dust. An added factor is that powdered coal of practically any grade can be converted to synthesis gas regardless of its tendency to cake, ash content, etc.
A typical example of a coal-gasification process using powdered coal is the Texaco process. In this process, comminuted coal is ground in a mill and then fed to a suspension tank. There a stable, pumpable suspension is prepared by the addition of fresh and recycled water. The coal suspension is pressurized by means of a pump and continuously fed to the burner at the top of the gasification reactor. Such a process is described in German Pat. No. 20 44 310, for example.
The measurement of temperatures in such reactors poses considerable difficulties. One difficulty is due to the extremely aggressive atmosphere, which militates against the use of thermocouples since these are rapidly embrittled by the action of high-temperature hydrogen. Other problems arise from the slag contained in the coal, which in the molten form destroys the protective tubes of thermometers or, when pyrometers are used, can result in deposits in the mesuring duct. Such deposits will produce distortion in the temperature measurements obtained from a pyrometer. The accuracy of measurement is adversely affected also by the fact that in the cooler zones of the reactor the carbon monoxide decomposes into carbon dioxide and carbon in accordance with the Boudouard equilibrium. The particulate carbon can result in the formation of a film which absorbs the radiation to be measured and thus results in false measurements.